I don’t quite understand what keeps this thread alive. The scope that we agreed at on the last call reads: “The scope of this project is to amend IEEE Std 802.3 to add physical layer specifications and management parameters for symmetric and/or asymmetric operation at 25 Gb/s, 50 Gb/s, and 100 Gb/s MAC data rates on point-to-multipoint passive optical networks.”

People are proposing alternative wording, but no one (except Frank) says what is wrong with the existing text. Frank’s concern is that 50Gb/s MAC is a new MAC speed and it may cause negative reaction from 802.3 voters. This is a valid concern, though I disagree that it will be problematic. And even if it is, I would rather hear about this when we try to approve PAR, instead of spending few years putting this in the draft and being unable to pass the sponsor ballot (if someone argues that 50G exceeded the scope).

But here is the thing: adding text like “in 25Gb/s steps” does not eliminate the new MAC speed. It makes the situation even worse, because this scope allows two new speeds 50G and 75G. So, if mentioning 50G MAC was concerning to some, this wording should be even more so.

Before we continue the endless loop of trying different gimmicks, let’s just restate what we want to standardize. Treat the following as a non-binding poll. It is not a lower bound as in the objectives, it is not an upper bound as in the PAR scope. This poll is to find out just the exact set of MAC speeds that each of us would like to see in the final standard. Once we all agree on what flavors of NG-EPON we want in the final specification, writing the appropriate scope will be much easier.

My argument for these (and only these) three speeds is that it gives nice ~2x generational improvement 10à25à50à100, so that EPON generations are approximately equally spaced. Going to smaller steps would split the markets. It would be tempting to wait over 50G and go from 25 to 75. Or wait over 75 and go from 50 to 100. Think of what happened with XG-PON1. Also, smaller steps (more frequent generations) confuse component vendors. Will they invest in 50G optics, or should they go directly to 75? If anyone thinks we need more speeds, please share your arguments.

3rd generation: 100/25, 100/50, 100/100 (100/10 could be too asymmetric to bother with, but still could be another option)

My assumtion here is that one upstream wavelength @ 25G is cheaper than two upstream wavelength @ 10G, i.e., that 50/25, 100/25, and 100/50 are respectively cheaper than 50/20, 100/20, and 100/40. But if this is not the case, current scope is flexible enough to allow nx10G upstream.

If we do 10Gb/s already in 10GPON and the IEEE standard for 100GbE is agreed at 25Gb/s channels then we should be concentrating on using a multiplier for the 25Gb/s rate up to 100Gb/s in 25Gb/s steps….

If we use 10Gb/s as the step that applies to the increase in bandwidth, where does that leave us with 25Gb…that is where does the 5Gb increase come from…10Gb/s…20Gb/s…25Gb/s…30Gb/s (this does not work). We should stick with the base of 25Gb/s and increase from there are 25Gb/s multiples…

I am fine with that, but it does not address the point that David brought up at the last call, i.e., anybody interested in intermediate data rates is not advised about their existence. That was the reason why we introduced “50 Gb/s” into the original scope after the last call.

Regarding your first question, as I understand it the scope is more of an upper bound, while our objectives are more of a lower bound. So while the 802.3 WG might be fine with the task force exceeding the objectives to create a 50 Gb/s option, the larger 802 group may not. To me this seems contrary to the way most of us do our jobs, because we all set objectives and then try to exceed them, but in this case it doesn’t necessarily fit the process established by IEEE.

Your second question is definitely a valid one. Would this be an acceptable scope?

My point - If the scope is not acceptable, then how are the objectives acceptable? Or, more accurately, if the objectives are acceptable, then why isn’t the scope written the same way as the objectives?

Is that now a concern for the Objectives, also - that they are not precise enough?

I think the current objectives are perfectly fine for what we actually want to accomplish. We want to be able to define flexible rates anywhere between 25Gb/s and 100Gb/s. I would add further clarification of the allowed increments to keep it to 25Gb/sec increments and (maybe) 10Gb/sec increments.

Is this approach not allowed by some rule?

Otherwise we are right back to where we were on Monday evening in Florida - making a table of the allowed rates.

The issue with the “reduced rates” statement is that it is not precise enough. Does it mean it would operate at 60 Gb/s, 40 Gb/s, 20 Gb/s or some intermediate speeds? This is the reason we ended up considering adding intermediate speed of 50 Gb/s to clearly delineate what the intermediate speed would be (lower rate)

I am lacking a lot of context for this conversation because I was unable to join the Thursday call. However, this seems to be nearly the exact discussion we had in Florida where those in attendance finally agreed to the objective:

We all agreed in Florida that it covers similar concerns expressed at that meeting. Those same concerns are being expressed here, so why not make the PAR scope substantially the same as the objective?

Something like this…

"The scope of this project is to amend IEEE Std 802.3 to add physical layer specifications and management parameters for operation on point-to-multipoint passive optical networks at a MAC data rate of 25 Gb/s and a MAC data of 100 Gb/s. The latter <may|will> also support operation at reduced MAC data rates."

Yes, I believe we have sufficient number of combinations and even as it is, we will have a field day narrowing them down to avoid designing too many flavors of PON.

I personally believe that it be sufficient to focus on 25/25G and 25/10G (if that has sufficient support), define it as a base PHY, and then just specify 2x and 4x stack of a base PHY. This would give us short term implementation goal (25G option) and long term goals for multiple lane systems(2x and 4x stacks of these), addressing the need for scalable architecture we discussed at the last Study Group meeting. It will keep us busy for quite some time to get this done right and building a very complex and comprehensive matrix of speeds … I do not see a value in that. There is little point in having multiple flavors of ONUs where we can get the job done with just a fewer of them. Economy of the scale is favor of limiting the number of speed options …

There was a conscious decision to exclude 75G, because it is too close to 100 and no self-respecting engineer (i.e., with a qualifying degree of OCD) will build a 3-channel solution instead of 4-channel one.

I completely agree that we don’t want to paint ourselves into a corner with the PAR. That said I think the proposed change to the PAR does exactly that – it allows for 25 Gb/s, 50 Gb/s and 100 Gb/s MAC data rates. The implaication here is that we don’t do, for example 75 Gb/s, or any other possible combination of 10 Gb/s & 25 Gb/s rates.

I like the thrust of Eugene’s suggestion; specifically state we will allow rates between 25 Gb/s & 100 Gb/s in increments of 10 Gb/s & 25 Gb/s. This really does state well what we want to be in scope.

I know how 10GEPON works. I even got an award for it. (And what luxury - a whole piece of 8.5x11 paper, with color printing, even!)

GK: Sorry, that’s all IEEE could afford. If you expect a more lavish award, you may consider participating in ITU-T J

Let’s not forget that everything in the standard is only a reference implementation. What you actually build is up to you, as long as it behaves as it should. This is particularly true for EPON.

So, for the concern on the “whole data path running at 100G” – come on… that’s not how it would be done.

Now, what’s wrong with saying that there is a 100G MAC, that then only uses a subset of its capability? In our view, that’s how you’d build any of these sub-rated things.

GK: True, with Tx throttling above the MAC and Rx gap filling below the MAC, a 100G MAC can support any effective data rate, even 1Mb/s, if you wish. But, given that the PAR scope defines a limit on what can be standardized, how would you justify having such reduced mode in the draft, without it being mentioned in the scope? It was discussed on the call which you missed. We can either take a risk at the PAR approval time by adding an intermediate speed, or we may take a risk at Sponsor Ballot time (a risk much higher, in my opinion) if we put such intermediate rate in the draft without the PAR scope “allowing” it.

I think there is a false argument here, that somehow people are going to build a dedicated 50G EPON. Do you think the industry is going to do such incremental advances? I don’t think so, particularly not for the silicon.

GK: Who knows what the future holds? To go from 25G to 100G is a big step. I don’t exclude that intermediate MAC speeds will be standardized and intermediate silicon speeds will be built.

Requiring the silicon to support 100G from day one will do nothing except pushing silicon availability several years out.

Another possible approach is to use existing 40G MAC with 2x25G PHY. This will nicely take care of all FEC and other EPON overheads, allowing true 40G data rates. But even with this approach, an operation at reduced PHY capacity should be supported by PAR scope, I think.

We expect that the 25G single channel technology will be developed, and that a way to combine them into higher speeds will be developed.

The 100G MAC is the large enough bucket that can accommodate 4 25’s, and four is a proven modularity.

And so, anybody who is interested in building any of these sub-rated systems would end up using 100Gb/s switch-ports.

I can say that some of this may depend on exactly how the channel combining is done. Some people may be thinking of “hard bonding” – that is, the designer decides how many channels will be tied together, and once they are combined, any ONU that wants to use those channels must listen to all of them. This is how 100G Ethernet works, and that is fine for point to point. They become an indivisible block, and that (maybe) motivates the thinking about a 50G MAC. I think this is a very poor design choice for PON. The whole point of PON is to allow bandwidth flexibility. It is much better to have a scheme of “soft bonding” – that is, the operator decides which ONUs work on which set of channels, and it can change over time. In addition, it is likely that there can be 1, 2, and 4 channel ONUs, all sharing the available channels in an efficient manner. If one “hard bonds” 2 channels together, then the single channel ONUs can’t listen to those channels – you’d have to have a single channel to take care of them. And then there is no space for the 4 channel bonded group. We would quickly paint ourselves into a corner.

GK: Agree, a protocol should be flexible to not waste network resources. Even more, sometimes the OLT may decide to communicate with an ONU on fewer wavelength than the ONU can support.

So, back to the scope: If the scope is a maximum, then 100G is a fine maximum. If we do the right thing regarding how the 100G MAC gets reduced, all the desired use cases will be supported. And that is what really matters.

10G-EPON uses exactly the same MAC as is used in 10G point-to-point. This MAC runs at exactly 10Gb/s, no matter what the actual data throughput. The PHY adds an overhead due to FEC, so the effective throughput is lower. The data is throttled above MAC to make sure it does not overrun PHY capacity. But the MAC spits bits (idles if there is no data) out at exactly 10Gb/s. In other words, the data path in 10G-EPON runs at 10Gb/s.

Since the PAR scope is the upper bound and what the project is allowed to cover (as David clarified on the call), the existing scope limits us to only 25G and 100G MACs and nothing else.

If we don’t add 50G MAC, then we will have the MAC and the entire data path running at either 25Gb/s or 100Gb/s, no matter how many wavelengths are activated. This is what we try to avoid. We need to allow another generation between 25G and 100G.

oGroup was asked to consider high level areas for which a lead would be identified to drive the contributions and decisions for that area. Examples are architecture, features, baseline, etc.

oThis would be different from creating ad hoc committees. While less formal than ad hocs, there would be improved organization with leads identified

oTask force members can contribute wherever they want – there are no restrictions.

·Miscellaneous

oScope of PAR: might need to add something to the scope to allow for rates between 25G and 100G, or something about degraded rates. Exceeding the scope by doing 50G, for example, when we’ve only mentioned 25G and 100G, could bring some “no” votes because it doesn’t match the scope.

oRisk: if we don’t change the scope, then we risk not getting approval in 2 years when we do sponsor ballot. If we do change the PAR, people might think it’s too big of a change and vote no. The commenting process is used to make changes to the PAR all the time. We need to make sure we have a good story regarding these changes.

oGroup initially considered scope as a minimum, which allowed operation at 50 Gbps, but it turns out this is not the case. The scope places upper bounds on the project.